2.2.6 References

2.2.6 References

This field lists the message ID's of
any articles prompting the submission of this article. It
is required for all follow-up articles, and forbidden when
a new subject is raised. Implementations should provide a
follow-up command, which allows a user to post a follow-up
article. This command should generate a Subject line
which is the same as the original article, except that if
the original subject does not begin with "Re: " or "re: ",
the four characters "Re: " are inserted before the
subject. If there is no References line on the original
header, the References line should contain the message ID
of the original article (including the angle brackets).
If the original article does have a References line, the
followup article should have a References line containing
the text of the original References line, a blank, and the
message ID of the original article.

The purpose of the References header is to allow articles
to be grouped into conversations by the user interface
program. This allows conversations within a newsgroup to
be kept together, and potentially users might shut off
entire conversations without unsubscribing to a newsgroup.
User interfaces may not make use of this header, but all
automatically generated followups should generate the
References line for the benefit of systems that do use it,
and manually generated followups (e.g. typed in well after
the original article has been printed by the machine)
should be encouraged to include them as well.